Analysis of Ionic Transport and Electrode Interfacial Reaction, and NMR One-Dimensional Imaging of Ether-Based Polymer Electrolytes

Abstract

Polyether-based polymer electrolytes containing an M x [N(SO2CF3)2] salt (x = 1 for Li and Na, 0.5 for Mg and Ca) were investigated for their thermal stabilities and ionic conductivities, owing to their high electrochemical stability and interfacial compatibility at electrodes as the electrolyte layer of all-solid-state batteries. The properties of an electrolyte / Na metal electrode interface were also explored. The thermal stability and ionic conductivity exhibited a strong correlation with the Coulombic interaction energy originating from cationic-radii and charge density derived from the cation’s valance number. The ionic conductivity of random copolymers of poly(ethyleneoxide) and poly(propyleneoxide) (P(EO/PO)) electrolytes increased slightly with decreasing cationic radii and decreased appreciably with valence number. In the [metallic electrode ∣ polymer electrolyte ∣ metallic electrode] cells, the interfacial resistances and their apparent activation energies at the polymer electrolyte / metallic electrode interfaces tended to be higher for the Na systems than for the Li systems. The calculated Na+ transport number exhibited a local maximum value when [Na]/[O] ∼0.04. To further evaluate the diffusive properties of active ions, nuclear magnetic resonance one-dimensional imaging was performed. The self-diffusion coefficient of TFSA was confirmed to correspond to the valence number of cation in the P(EO/PO)-M x [N(SO2CF3)2] electrolytes.